Class G amplifiers refer to the class of amplifiers that dynamically switch supply voltages to improve on the amplifier's power efficiency. The Class G amplifiers are a modification of another class of amplifier (normally Class B or Class AB) to increase efficiency and reduce power dissipation. Class G amplifiers take advantage of the fact that musical and voice signals have a high crest factor with most of the signal content at lower amplitudes. Conventional Class G amplifiers use multiple power supplies, operating from the power rail that provides the optimum power dissipation.
A Class G amplifier uses a minimum of two different supply rails. The device operates from the lower supply until a higher supply is needed. At this point the device switches the output stage to the higher supply rail. Once the output signal drops below a predetermined level, the device switches back to the lower rail.
There are a number of trade-offs associated with Class G amplifiers: selecting the proper number of supplies and the voltage difference between the supplies to optimize at lower voltages, while minimizing power dissipation. Two different rails minimize the complexity of the power supplies, while providing sufficient voltage flexibility. Additional rails may reduce power dissipation further but at the cost of higher component count, complexity, and reliability. Another issue is the length of time the device operates from the higher rail. While operating from the higher supply rail, power dissipation increases. Switching back to the lower rail too early may result in distortion due to clipping, while remaining at the higher rail for an extended period of time will result in a degradation of efficiency.
Embodiments of the invention address these and other limitations in the prior art.